The invention relates to circulating pumps for flowable thermal or heat carriers in heating systems.
The output of a circulating pump is defined by the product of pressure and quantity. Multiplied by the temperature drop that the thermal carrier experiences in the heating system, the quantity in turn produces the heating capacity transmitted by the thermal carrier. Conventional heating systems function with a high temperature gradient between the forward feed and the runback, consequently requiring relatively low hydraulic circulation capacities. Given heating systems supplied by low-temperature boilers, by heat pumps or by solar collectors, however, the cost of heat is all the lower the lower the forward feed temperature is set, and thus the smaller the temperature gradient is between the forward feed and the runback. Heating systems having such heat sources accordingly function with high volume flows, therefore requiring high hydraulic circulating capacities. The annual power consumption for the circulating pumps given heating systems with energy-saving heat generators is therefore considerably higher than in older systems. The pumps therefore become the critical energy user, this having a particularly deletorious effect given energy-saving heating systems.
The intersection of the pressure/quantity curve of the pump and the resistance characteristic of the system forms the operating point that is displaced toward higher pressures the smaller the system or the higher its resistance.
Heat pumps having pole-change motors are known. Multiple pole change-overs effect a switching of the motor to half its speed as soon as a prescribed temperature in the heating system is downwardly transgressed. These pumps, however, only allow a two-position control with a power jump of 8:1 and require expensive motors.
Pumps having phase controls have also been disclosed. Phase-control operation involves the disadvantage that it generates considerable radio interference and that the motor starting torque decreases proportionally with the working torque, whereby the jeopardy of jamming during start-up increases considerably.